The present invention relates to a basic formula of an active layout drawing in pants tailoring, and more particularly, a basic formula to measure the figure of human body so as to alternatively fit the differences in body figure. Regular layout drawing in tailoring does not change and cannot help to discover the defect in body figure for compensation in advance, thereby misfits happen quite often and further alteration is usually required. Another object of the present invention is to provide an active layout drawing technique such that the dressmaker can easily handle with the variation in body figure while tailoring to prevent any further alteration.